Improved Element for Processing Solar Radiation, and a Sun Tracker and a Solar Farm Equipped with Such an Element

ABSTRACT

An element for processing solar radiation includes means for processing solar radiation forming a layer of the solar radiation processing element and includes a layer of radiation-emitting material, especially infrared radiation, covering the layer of the processing means. A sun tracker includes at least one processing element and a solar farm includes a series of sun trackers, each comprising a processing element.

The invention relates to an element for processing solar radiation improved to emit infrared radiation. It also relates to a solar tracker comprising such an element. Lastly, the invention also relates to a concentrated solar power plant equipped with such solar trackers.

In the context of concentrated solar power (CSP) plants, a thermodynamic cycle implemented in a CSP plant produces what is referred to as low-temperature-level waste heat that must be evacuated via the condenser of the CSP plant. Typically, the temperature level is about 55° C. and the heat produced is about 2 thermal megawatts for 1 megawatt of generated electricity. At the present time, this extraction of heat is achieved by way of water towers that consume substantial amounts of water, about 3.5 to 4 m³ of water per MWhe. Such a water consumption is unacceptable in arid regions that are liable to be suitable for such CSP plants. An alternative to the use of water towers consists in extracting the heat by exchange with the ambient air using forced convection exchangers. However, the use of forced convection exchangers is conditional upon the ambient temperature being close to the condensation point. Thus, the use of forced convection exchangers does not allow under-cooling to be achieved and induces a decrease in the thermodynamic efficiency of the thermodynamic cycle implemented by the CSP plant of about 2 to 3%, and an increase in the cost of the electricity thus generated of about 3 to 8%. Furthermore, in CSP plants, regular cleaning of the mirrors of the solar field is indispensable and represents a large investment in terms of man-hours, on the one hand, and, on the other hand, requires water representing about 2% of the total water consumption of the CSP plant in question to be used.

One aim of the invention is to provide a system allowing the aforementioned problems to be solved.

For this purpose, provision is made, according to the invention, for an element for processing solar radiation comprising means for processing solar radiation forming a layer of the element for processing solar radiation, and a layer of material emissive of radiation, especially infrared radiation, covering the processing means layer.

Thus, the use of a layer of material emissive of radiation, such as infrared radiation, covering the processing means layer of the processing element makes it possible to obtain an emission of radiation directed toward space, which acts as a cold body (because it has a temperature of about 3° K, i.e. −270° C.), and therefore makes it possible to evacuate heat by radiation from the element for processing solar radiation toward space. Such an evacuation of heat consumes no water to this end.

Advantageously, but optionally, the processing element according to the invention has at least one of the following technical features:

-   -   the processing element furthermore comprises a layer forming a         heat exchanger located under and covered by the processing means         layer;     -   the processing element furthermore comprises an insulating lower         layer;     -   the layer forming a heat exchanger comprises in a thickness a         network of ducts in which a heat-transfer fluid flows and         comprising a fluid inlet and a fluid outlet; and     -   the layer of emissive material is produced by a surface         treatment of a surface of the processing means layer.

Provision is also made, according to the invention, for a solar tracker comprising a structure movably mounted on a construction implanted in a ground portion, comprising at least one processing element having at least one of the above technical features.

Advantageously, but optionally, the solar tracker has at least one of the following additional technical features:

-   -   the solar tracker furthermore comprises means for collecting         water trickling over the layer of emissive material of the         processing element;     -   the solar tracker is controlled by a system for controlling an         orientation of the structure, the control system being arranged         so as to adapt the orientation of the solar element depending on         climatic conditions around the processing element; and     -   the solar tracker furthermore comprises means for fluidically         connecting the layer forming a heat exchanger with a geothermal         exchanger buried in the ground portion.

Provision is also made, also according to the invention, for a concentrated solar power plant comprising a condenser equipped with a heat exchanger, and a series of solar trackers having at least one of the above technical features.

Advantageously, but optionally, the concentrated solar power plant has at least one of the following additional technical features:

-   -   the layers forming a heat exchanger of each of the processing         elements of the series of solar trackers are fluidically         connected to one another so as to form a single cooling circuit;         and     -   the heat exchanger of the condenser is fluidically connected to         the single cooling circuit.

Other features and advantages of the invention will become more apparent from the following description of an embodiment of the invention. In the appended drawings:

FIG. 1 is a schematic cross-sectional view of an element for processing solar radiation according to the invention;

FIG. 2 is a schematic cross-sectional view of a first embodiment of a solar tracker according to the invention comprising processing elements such as shown in FIG. 1;

FIG. 3 is a schematic cross-sectional view of a second embodiment of a solar tracker according to the invention comprising a processing element such as shown in FIG. 1;

FIG. 4 is a schematic view of an installation and connection of at least two solar trackers such as shown in FIG. 3;

FIG. 5 is a schematic view illustrating a cooling circuit of a CSP plant according to the invention comprising a field of solar trackers such as shown in FIG. 3; and

FIG. 6 is a schematic view illustrating a solar plant equipped with solar trackers, according to the invention.

With reference to FIG. 1, an element 10 for processing solar radiation according to the invention will now be described. The element 10 for processing solar radiation according to the invention comprises means for processing solar radiation forming a layer 2. These means for processing solar radiation are a reflective mirror in the context of an application to a concentrated solar power plant. As a variant embodiment, the means for processing solar radiation may be photovoltaic cells or any other device allowing solar radiation received by the element 10 for processing solar radiation according to the invention to be processed.

The element 10 for processing solar radiation according to the invention furthermore comprises a layer 1 of material emissive of radiation. This layer 1 of material emissive of radiation is produced so as to cover the processing means layer 2 of the element 10 for processing solar radiation according to the invention. This layer 1 of material emissive of radiation forms a thin film that is added to an upper surface of the processing means layer 2. As a variant embodiment, the layer 1 of material emissive of radiation is produced by a surface treatment of the upper surface of the processing means layer 2. The one or more materials used to produce the layer 1 of material emissive of radiation are chosen so as to optimize the emission of radiation E_(R) at a certain wavelength that allows thermal energy to be exchanged with space through the Earth's atmosphere, once the element 10 for processing solar radiation according to the invention has been installed on a portion of the Earth's surface. The wavelength of the radiation E_(R) enabling such heat exchange is in the wavelengths of the infrared, in particular and preferably between 8 and 16 μm. This makes it possible to optimize the heat exchange that occurs naturally between two bodies having two surfaces facing each other and the temperatures of which are different. Specifically, a radiative heat exchange thus takes place and is dependent on the difference in the power 4 of the temperatures of the two facing bodies. The layer 1 of material emissive of radiation may be produced using a lacquer or a laminated plastic film, or even be made of glass. Thus, it is possible to obtain a radiative heat exchange of about 50 W/m².

Furthermore, the element 10 for processing solar radiation according to the invention comprises a layer 3 forming a heat exchanger. This layer 3 forming a heat exchanger is positioned on a lower surface of the processing means layer 2, which lower surface is opposite the upper surface of the processing means layer 2 that receives the layer 1 of material emissive of radiation. This layer 3 forming a heat exchanger here comprises a network of ducts 5 winding under and making thermal contact with the lower surface of the processing means layer 2 of the element 10 for processing solar radiation according to the invention. The network of ducts 5 forms a single circuit and comprises an inlet 7 and an outlet 6 in order to allow a heat-transfer fluid to be made to flow within the network of ducts 5 forming the layer 3 forming a heat exchanger. The network of ducts 5 may be embedded in a material promoting heat exchange between the lower surface of the processing means layer 2 and the network of ducts 5 in which the heat-transfer fluid flows between the inlet 7 and the outlet 6.

Lastly, the element 10 for processing solar radiation according to the invention comprises an insulating lower layer 4 positioned below the layer 3 forming a heat exchanger. This insulating lower layer 4 makes it possible to minimize heat exchange between the ground above which the element 10 for processing solar radiation according to the invention is installed and said element 10 for processing solar radiation according to the invention. In addition, this insulating lower layer 4 makes it possible to promote and protect heat exchange between the processing means layer 2 and the layer 3 forming a heat exchanger.

In use, the element 10 for processing solar radiation according to the invention allows heat to be exchanged without the consumption of water being necessary. Heat is exchanged, using the emission of radiation E_(R), with space. Furthermore, heat is naturally transferred by convection between the upper surface of the element 10 for processing solar radiation according to the invention and the atmosphere. Lastly, heat exchange occurs with the layer 3 forming a heat exchanger.

During the day, the element 10 for processing solar radiation according to the invention will make it possible to maintain an optimal operating temperature for the means for processing solar radiation that form the layer 2 of the element 10 for processing solar radiation according to the invention. In the context of a use in a CSP plant, the network of ducts 5 of the element 10 for processing solar radiation according to the invention is fluidically connected to a heat exchanger of a condenser of the CSP plant and thus it is possible for the production of heat referred to as low-temperature-level waste heat to be evacuated via this condenser.

During the night, the structure of the element 10 for processing solar radiation according to the invention will allow the temperature of the upper surface of the layer 1 of material emissive of radiation of the element 10 for processing solar radiation according to the invention to be decreased below the dew point temperature. This will make it possible to condense, on this upper surface of the layer 1 of material emissive of radiation of the element 10 for processing solar radiation according to the invention, moisture contained in the ambient air. The water thus formed on the surface will allow this surface to be cleaned naturally. In addition, if a large amount of water is thus produced by condensation, the surplus is collected for subsequent use. This production of water is about 200 to 1000 liters for every 500 m² of area of element 10 for processing solar radiation according to the invention.

With reference to FIG. 2, we will now describe a solar tracker according to the invention employing an element 10 for processing solar radiation according to the invention. The solar tracker 20 according to the invention is here a parabolic solar tracker comprising two elements 10 for processing solar radiation according to the invention, which are preferably curved in order to form a parabola. The layer 1 of material emissive of radiation of the element 10 for processing solar radiation according to the invention is located on the interior of the parabola formed by the element 10 for processing solar radiation according to the invention, whereas the insulating lower layer 4 is positioned on the exterior of the solar tracker 20 according to the invention. Thus, since the processing means layer 2 here forms a mirror, solar radiation is reflected by the element 10 for processing solar radiation according to the invention toward a focal point of the parabola formed by this element 10 for processing solar radiation according to the invention. The focal point is occupied by a tubular furnace 21 in which flows a heat-transfer fluid that collects the solar energy thus reflected by the element 10 for processing solar radiation according to the invention of the solar tracker 20 according to the invention. The two elements 10 for processing solar radiation according to the invention, forming the solar tracker 20 according to the invention, are positioned side-by-side so as to form a basin and are separated, at a low point, by a passage 23. Under this passage 23, the solar tracker 20 according to the invention comprises means for collecting trickling water 22, here taking the form of a drain pipe. Thus, as indicated above, overnight the condensation that forms on the exterior surface of the layer 1 of material emissive of radiation of the two elements 10 for processing solar radiation according to the invention trickles toward the low point, and therefore toward the passage 23, then flows naturally into the drain pipe 22 that allows excess trickling water to be collected by a device for putting this water to use. In addition, as it trickles, this water cleans the elements 10 for processing solar radiation according to the invention.

Now, with reference to FIG. 3, we will describe a second embodiment of a solar tracker according to the invention comprising an element 10 for processing solar radiation according to the invention. The solar tracker 30 according to this second embodiment of the invention is here a flat solar tracker comprising an element 10 for processing solar radiation according to the invention installed on a structure 31 itself pivotably mounted on a construction 32, for example taking the form of a pole, allowing the solar tracker 30 according to the invention to be installed on a ground portion S of a site. Again, on at least one edge, the solar tracker 30 comprises means for collecting trickling water 22, here again taking the form of a drain pipe. Operation overnight is identical here as for the solar tracker 20 according to the invention of the first embodiment described above. In order to ensure the water trickles, the tracker 30 according to the invention may allow the element 10 for processing solar radiation according to the invention, which here forms a plane, to be inclined by an amount that enables this trickling to be achieved.

In the case of the solar tracker 20 according to the first embodiment and of the solar tracker 30 according to the second embodiment, the orientation of the elements for processing solar radiation according to the invention is achieved, in a way known per se, by a system for controlling an orientation of the structure (not shown), which allows the structure of the solar tracker and therefore the elements 10 for processing solar radiation according to the invention to be oriented so that the radiation emitted by the sun during the day strikes the element 10 for processing solar radiation according to the invention at an optimal angle. This control is carried out during daylight hours. However, in order to optimize operation overnight, the system for controlling an orientation of the structure is used to orient consequently the elements 10 for processing solar radiation according to the invention in order to optimize heat exchange, on the one hand, and above all, on the other hand, to optimize the production of water. To do this, the system for controlling an orientation of the structure orients the elements 10 for processing solar radiation according to the invention depending on the meteorological conditions in the vicinity of the element 10 for processing solar radiation according to the invention, in particular depending on wind strength/direction as wind has a tendency to dry the water obtained by the condensation. Furthermore, the system for controlling an orientation of the structure allows, at regular intervals overnight, the inclination of the elements 10 for processing solar radiation according to the invention to be abruptly changed for a short period of time so as to cause the water condensed on the surface of the element 10 for processing solar radiation according to the invention to trickle and to ensure that this water trickles toward the means 22 for collecting trickling water, which means are installed on the solar trackers controlled by the system for controlling an orientation of the structure.

With reference to FIG. 4, we will now describe an arrangement of two solar trackers according to the invention equipped with elements 10 for processing solar radiation according to the invention. Each of the solar trackers 30 according to the invention here comprises, within its construction 32, a geothermal exchanger buried in the ground S on which the solar trackers 30 according to the invention are installed. This heat exchanger is optional in the arrangement of two solar trackers according to the invention. Here, the geothermal exchanger is produced using feet of the construction 32 which take the form of two coaxial tubes 324 and 323. The two tubes 323 and 324 are designed to allow a heat-transfer fluid to be made to flow therein and thus form a geothermal exchanger in one portion of the feet of the construction 32, said portion being buried in the ground S. Thus, when the solar tracker 30 according to the invention is put in place on the ground portion S, the fluid outlet 6 of the element 10 for processing solar radiation according to the invention is connected to an inlet 321 of the interior tube 323 whereas an outlet 322 of the external tube 324 is connected to the inlet 7 of the element 10 for processing solar radiation according to the invention. Thus, the heat-transfer fluid flowing in the network of ducts 5 of the layer 3 forming a heat exchanger, after having absorbed heat from the element 10 for processing solar radiation according to the invention, especially if it is a question of an element comprising photovoltaic cells, will flow through the geothermal exchanger in the tubes 323 and 324 and transmit this heat to the ground S via an exchange E_(S) of heat. Thus, the cooled heat-transfer fluid is reinjected through the inlet 7 into the element 10 for processing solar radiation according to the invention. In the case illustrated in FIG. 4, it is possible to connect the various solar trackers of a solar field to one another. To do this, the inlet 7 of the first solar tracker 30 according to the invention is connected to a supply duct 40 for example originating from another solar tracker. The outlet 6 of the first solar tracker 30 according to the invention is connected to the inlet 321 of the geothermal exchanger of this first solar tracker 30 according to the invention. The outlet 322 of the geothermal exchanger of the first solar tracker 30 according to the invention is connected to the inlet of the element 10 for processing solar radiation according to the invention of the second tracker 30 according to the invention using a duct 42. Next, the outlet 6 of the element 10 for processing solar radiation according to the invention of the second solar tracker 30 according to the invention is connected to the duct 43 at the inlet of the thermal exchanger of the second solar tracker 30 according to the invention. The outlet of the heat exchanger of this second solar tracker 30 is connected to the following solar tracker using a duct 44 and so on.

In the situation where the trackers 30 of the arrangement of solar trackers according to the invention do not comprise geothermal exchangers, the outlet 6 of the first solar tracker 30 is directly connected to the inlet 7 of the second solar tracker 30.

The above description with regard to a solar tracker 30 according to the invention is applicable in an identical way to an array of solar trackers 20 according to the invention.

With reference to FIG. 5, we will now describe the connection of an exchanger 100 of a condenser of a CSP type condensation solar power plant comprising a solar field including elements 10 for processing solar radiation according to the invention installed on solar trackers of the solar field of the CSP plant. The various elements 10 for processing solar radiation according to the invention of the solar field are connected to one another as described above with reference to FIG. 3. Except that the outlet 6 of the heat exchanger of the last solar tracker 30 according to the invention is connected to an inlet of the exchanger 100 of the condenser of the CSP plant via the duct 44 whereas an outlet of the exchanger 102 of the condenser of the CSP plant is fluidically connected by the duct 40 to the inlet 7 of the first solar tracker 30 of the solar field. A three-way valve 101 is installed at the inlet of the exchanger 100 of the condenser of the CSP plant an outlet of which is connected using a duct 103 to the outlet of a second three-way valve 102 installed at the outlet of the exchanger of the condenser of the CSP plant. The use of these three-way valves 101, 102 and of the duct 103 makes it possible to prevent, if required, the heat-transfer fluid from passing through the exchanger 100, which is useful during overnight operation when the condenser of the CSP plant is not in operation.

FIG. 6 illustrates, schematically, a CSP type condensation solar power plant equipped with a plurality of elements 10 for processing solar radiation, namely two in the example shown, each formed from a mirror that concentrates solar radiation on a tubular collector 105. These collectors are mounted in series and passed through by the heat-transfer fluid that forms the heat source of the evaporator exchanger 107 of the plant. This heat-transfer fluid is heated by absorption of the solar radiation reflected by the elements 10 for processing solar radiation. A pump 107 pumps the heated fluid into the evaporator exchanger 107 of the plant. In the evaporator exchanger 107, the heat-transfer fluid heated by the elements 10 serves to produce steam. This pressurized steam drives the electricity generating turbine 111 of the plant. The low-pressure steam output from the turbine 111 is then condensed by way of the condenser exchanger 100. The working fluid is made to flow by a pump 115 that increases the pressure of the fluid in this closed circuit. According to the invention, it is the fluid flowing under the effect of a pump 117 through the heat exchangers of the elements 10 for processing solar radiation that serves as a cold source in the heat exchanger 100. The heat absorbed during the condensation is transferred to the exterior by the elements 10 for processing solar radiation, on the one hand by convection, and on the other hand by radiation by virtue of the layer of emissive materials, which especially emit infrared radiation.

It should be noted that the cooling circuit formed by the heat exchangers of the trackers may also comprise supporting constructions taking the form of poles, in accordance with FIG. 5.

Thus, in the context of a CSP plant, the use of elements 10 for processing solar radiation according to the invention on solar trackers forming the solar field of the CSP plant allows said solar field of the CSP plant to be used as a macro heat exchanger by associating the convective and radiative transfer described above. Thus, a considerable area of exchange is made available, about 10,000 to 13,000 square meters per MWhe, enabling the heat of condensation issued from the exchanger 100 of the condenser of the plant to be extracted, but also the thermodynamic cycle implemented by the CSP plant thus equipped to be under-cooled and the efficiency thereof thus to be improved. The solar field is thus exploited not only during the day but also during the night and its relative investment cost is therefore decreased by crossover. The invention such as described above allows the need to evacuate heat to be met without any water consumption and simultaneously allows the performance of the thermodynamic cycles implemented by the CSP plant thus equipped to be improved. On the whole, the water consumption of the CSP plant thus equipped is thus decreased by more than about 90%. Because there is no need for any water tower to cool the thermodynamic cycle. Furthermore, the use of the surfaces of the elements 10 for processing solar radiation according to the invention equipping the solar field as radioactive exchange surfaces overnight also allows ambient moisture to be condensed from the surrounding air. Thus, the condensates formed flow gravitationally into the means 22 for collecting trickling water equipping the various solar trackers of the solar field, cleaning the upper surface of the elements 10 for processing solar radiation according to the invention. The water thus produced is collected by the means 22 for collecting trickling water and then easily put to use. The solar field is then no longer the origin of water consumption but an actual producer of this usable water and the elements for processing solar radiation are therefore cleaned without any need for human intervention.

Of course, it is possible to make many modifications to the invention without however departing from the scope thereof.

In particular:

-   -   the layer 1 emissive of radiation may be arranged on a back side         of the element 10 for processing solar radiation. In this case,         the element 10 for processing solar radiation does not comprise         an insulating lower layer 4 since the latter is replaced by the         layer emissive of radiation. When this variant embodiment of the         element for processing solar radiation is used in a solar         tracker, radiation E_(R) is emitted when the system for         controlling the solar tracker flips said solar tracker so as to         position the back side of the element for processing solar         radiation, and therefore the layer emissive of radiation then         arranged on this back side, facing space; and     -   in the context of a linear Fresnel solar tracker, the network of         ducts 5 of the layer forming a heat exchanger is arranged in an         axle bearing the element for processing solar radiation,         generally comprising a mirror. 

1-12. (canceled)
 13. An element for processing solar radiation comprising: a means for processing solar radiation layer and a layer of material emissive of radiation covering the processing means layer.
 14. The processing element of claim 13, further comprising a layer forming a heat exchanger located under and covered by the processing means layer.
 15. The processing element of claim 14, further comprising an insulating lower layer.
 16. The processing element of claim 14, wherein the layer forming a heat exchanger comprises, in a thickness, a network of ducts in which a heat-transfer fluid flows and comprising a fluid inlet and a fluid outlet.
 17. The processing element of claim 13, wherein the layer of emissive material is produced by a surface treatment of a surface of the processing means layer.
 18. A solar tracker comprising a structure movably mounted on a construction implanted in a ground portion (S) and at least one processing element according to claim 13 mounted on the structure.
 19. The solar tracker of claim 18, further comprising means for collecting water trickling over the layer of emissive material of the processing element.
 20. The solar tracker of claim 19, wherein the solar tracker is controlled by a system for controlling an orientation of the structure, the control system being arranged so as to adapt the orientation of the solar element depending on climatic conditions around the processing element.
 21. The solar tracker of claim 20, further comprising means for fluidically connecting the layer forming a heat exchanger with a geothermal exchanger buried in the ground portion.
 22. A concentrated solar power plant comprising a condenser equipped with a heat exchanger and a series of solar trackers as claimed in claim
 21. 23. The concentrated solar power plant of claim 22, wherein the layers forming a heat exchanger of each of the processing elements of the series of solar trackers are fluidically connected to one another so as to form a single cooling circuit.
 24. The concentrated solar power plant of claim 23, wherein the heat exchanger of the condenser is fluidically connected to the single cooling circuit.
 25. The element of claim 13 wherein the layer emissive of radiation is emissive of infrared radiation. 